1. Field of the Invention
The present invention relates to the technology field of digital camera and, more particularly, to an apparatus and a method for forecasting output voltage of a battery of a digital camera.
2. Description of the Related Art
Please refer to FIG. 4. FIG. 4 shows a power supply status of a conventional digital camera. For currently digital camera design, as shown in FIG. 4, the power consumptive elements of a digital camera are: a charging circuit of the flash 91, a back-light driving circuit of LCD display 92, and a driving circuit of lens motor 93. These power consumptive elements require large power consumption. Therefore, they need three switch units 911, 921, 931 to control the supply of power, respectively. During the operation of the digital camera, if the functions of these power consumptive elements are not necessary, the related switch will be turned off to stop supplying power. The other logic circuit 94 of the digital camera comprises a digital signal processor, a ROM (read-only memory), and a RAM (random-access memory). Because of the power consumption of these elements is less and their functions are always necessary for the camera operation, there is no power supply restraint for them.
The power of the digital camera is supplied by the battery 95. After the battery 95 has been used for a while, the output voltage of the battery 95 will gradually decrease. Therefore, in order to avoid the camera from being out of function or shut down due to the insufficient output voltage of the battery, a digital camera is generally installed with a battery low detection circuit 96. When the output voltage of the battery is lower than a predetermined threshold limit value, the digital camera will generate a warning signal or sound to inform the user to replace the battery. Since, the digital camera has the aforementioned power consumptive elements, when one of the power consumptive elements works, the output voltage of the battery will be decreased differently, which result in the battery low detection circuit 96 being unable to detect the actual output voltage of the battery. Therefore, it is desired to improve the design of the battery low detection circuit of the digital camera.
The objective of the present invention is to provide an apparatus and a method for forecasting the output voltage of a battery of a digital camera, so as to obtain the voltage drop of the output voltage of the battery caused by power consumptive elements, thereby being aware of the remaining power of the battery and obtaining the maximum power supplying efficiency for the digital camera.
In accordance with one aspect of the present invention, there is provided a n apparatus for forecasting output voltage of a battery of a digital camera. The apparatus comprises: a battery voltage detection circuit connected to two output ends of a battery for outputting a dividing voltage of the battery from a dividing voltage output end; an analog-to-digital converter connected to the voltage output end for converting an analog voltage value to a digital signal to output from its output end; a dummy load connected across on the two ends of the battery; and a central processing unit connected to the output end of the analog-to-digital converter for controlling whether to conduct the dummy load or not, so as to obtain output voltages of the dummy load during off condition and on condition, respectively, and, according to the obtained output voltage, determining an internal resistance of the battery for further determining an output voltage of the battery in operating at least a power consumptive element based on an internal resistance of the battery and pre-obtained power consumption of the power consumptive element.
In accordance with another aspect of the present invention, there is provided a method for forecasting output voltage of a battery of a digital camera. The camera comprises a dummy load connected across on two ends of a battery and a plurality of power consumptive elements. The method comprises the steps of: (A) disconnecting the dummy load after the digital camera is turned on; (B) obtaining an output voltage Vdoff of the battery during the dummy load is off; (C) conducting the dummy load; (D) obtaining an output voltage Vdon of the battery during the dummy load is on; (E) determining the internal resistance of the battery by (Vdoffxe2x88x92Vdon)*(RD/Vdon), wherein RD is resistance value of the dummy load; and (F) determining the output voltage of the battery in operating the power consumptive elements is Vdoffxe2x88x92(Vdoffxe2x88x92Vdon)*(RD*I(x)/Vdon), wherein I(x) is pre-obtained current consumption of the power consumptive elements corresponding to the output voltage of the battery.
Other objectives, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.